1. Field of the Invention
The invention relates to a method of operating a burner that is supplied with a quantity of a fuel by a fuel supply line. The fuel quantity is set by the degree of opening of a control element as a function of a selected output of the burner. The invention also relates to a corresponding burner configuration.
Various control systems for gas turbine burners are described in the book xe2x80x9cDie Gasturbine (The gas turbine)xe2x80x9d by J. Kruschik, Springer-Verlag, Vienna 1960, Second Edition, Pages 354 ff. Depending on the field of employment of the gas turbine, quite different configurations for the control systems exist. A common feature of the control systems is that a fuel supply to the burner is controlled, in each case, in accordance with a preselected output of the gas turbine. The control takes place, for example, as a function of rotational speed by a handling of a control element in a fuel supply line with a centrifugal force pendulum. In the example shown in Fig. 359 on Page 356 of Kruschik, the fuel quantity supplied to the burner is controlled as a function of the air pressure generated by the compressor of the gas turbine. In a further example shown in Fig. 361 on Page 358 of Kruschik, the fuel quantity to be burnt is controlled by a supply/return nozzle. Starting on Page 365 of Kruschik, a control system for the fuel supply to an aircraft turbine is described as particularly demanding because, in this case, it is necessary to deal with large temperature and pressure fluctuations in the external air.
In xe2x80x9cDubbel, Taschenbuch fxc3xcr den Maschinenbau (Machinery Handbook)xe2x80x9d, published by W. Baltz and K. H. Kxc3xctner, Springer-Verlag, 1990, 17th Edition, Section X15 6.4, it is stated that control elements for setting a mass flow of a medium cause a pressure drop as a function of the density and the velocity of the medium. From VDI/VDE Guideline 2173, the kV value (characteristic value of the valve) determined experimentally for each configuration characterizes the through-flow of incompressible media as a volume flow of water (density xcfx810) at temperatures between 5 and 30xc2x0 C. and a pressure drop xcex94pV0 of 0.98 bar. Arbitrary pressure drops xcex94pV and other densities xcfx81 provide the volume flow:             V      .        v    =            k      v        ⁢                            Δ          ⁢                      xe2x80x83                    ⁢                      p            v                    ⁢                                    p              0                        /                          (                              Δ                ⁢                                  xe2x80x83                                ⁢                                  p                  vo                                ⁢                p                            )                                          .      
The way in which the kV value depends on the setting parameter is the valve characteristic. For the completely open valve, kV is referred to the maximum value kVS. The value:             k      vs        =                            V          .                0            ⁢                        Δ          ⁢                      xe2x80x83                    ⁢                      p            vo                    ⁢                      p            /                          (                              Δ                ⁢                                  xe2x80x83                                ⁢                                  p                  v                                ⁢                                  p                  0                                            )                                            ,
with the maximum through-flow {dot over (V)}0, is provided by the valve manufacturer, for example.
It is accordingly an object of the invention to provide a method of operating a burner and burner configuration that overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices and methods of this general type and that provides a method of operating a burner with a supply of fuel based on a preselected output and a corresponding burner configuration.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a method of operating a burner, including the steps of supplying a burner with a quantity of a fuel through a fuel supply line, setting the fuel quantity by a degree of opening of a control element as a function of a selected output of the burner, determining a calorific value of the fuel, and calculating and directly setting the degree of opening using the output and the calorific value of the fuel.
The invention is based on the knowledge that a conventionally employed, iterative control of the fuel quantity supplied as a function of the preselected output is too sluggish relative to suddenly modified operational boundary conditions. In such an iterative control system, the degree of opening is controlled in steps for setting the preselected power. In other control systems, the required output is, for example, converted directly into a setting parameter that fixes the degree of opening by a mechanical system which, as a rule, is very complex. In such systems, there is generally very limited variability with respect to the reaction to modified boundary conditions because any conversion from the preselected power into the degree of opening takes place only by a preset, fixed mechanism.
In accordance with another mode of the invention, the burner of the invention can be a burner for a gas turbine, in particular, a stationary gas turbine, and also, for example, suitable for an internal combustion engine of a vehicle. Fuel for the burner can, for example, be: mineral oil, natural gas, diesel, gasoline, or kerosene.
For the invention, on the other hand, the degree of opening is first calculated based on the output and, then, is set directly. The invention provides the advantage of removing the need to carry out an iterative control. Consequently, there is a significantly faster system reaction. The system, therefore, reacts more rapidly to, for example, external perturbations such as a pump switching operation. An additional advantage is that it is possible to deal in a better and more variable manner with the current operating conditions because the degree of opening is calculated in a manner matched to the respective operating conditions. For example, modifications to the temperature, density, or type of fuel or a variable pressure at the location of the burner can be employed in a simple manner for regulating the fuel quantity to be supplied. Compared with control systems having a direct, mechanical conversion from the preselected output to the degree of opening, the invention provides a substantially increased flexibility with respect to modified boundary conditions.
The calorific value of the fuel is preferably determined and employed in the calculation of the degree of opening. It is preferable for a mixture of at least two materials to be used as the fuel. The calorific value of the fuel is employed in the determination of the fuel quantity required because the calorific value also determines an effective output from the combustion system. Such a determination of the calorific value is of particular advantage when a fuel mixture is used, possibly even with a composition that varies with time. An oil/water mixture is preferably used as the fuel, the energy consumption for any evaporation of the water being determined during the combustion and being employed in the calculation of the degree of opening. Such an oil/water emulsion or dispersion is used to reduce emissions of oxides of nitrogen. The average combustion temperature is reduced by the admixture of water. Part of the energy of the fuel is consumed by the evaporation of the water and does not, therefore, contribute to the desired output.
It is preferable for the density of the fuel to be determined and employed in the calculation of the degree of opening. The density of the fuel contributes to the determination of the mass flow of the fuel through the fuel supply line. The determination of the density of the fuel is of advantage, particularly when a fuel mixture is used.
A pressure loss in the fuel supply line is preferably determined and employed in the calculation of the degree of opening. Such a pressure loss contributes to the determination of the mass flow of the fuel through the fuel supply line so that the pressure loss is taken into account, in an advantageous manner, in the calculation of the degree of opening.
The burner preferably opens into a combustion chamber in which a combustion chamber pressure is present, the combustion chamber pressure being measured and employed in the calculation of the degree of opening.
The pressure in the combustion chamber has an effect on the quantity of fuel entering the combustion chamber. Particularly in the case of a gas turbine, the pressure in its combustion chamber is substantially higher than the ambient pressure because combustion air from a compressor is supplied to the combustion chamber.
For the control element, a through-flow comparison value is preferably determined at which, for the pressure conditions present, there is a fuel mass flow through the control element that leads to the selected output of the burner. The degree of opening is determined by a conventional relationship between the through-flow comparison value and the degree of opening. Such a through-flow comparison value is the kV value provided by the machinery handbook cited.
The burner is preferably configured for optional operation with at least two different fuels. Preferably, the burner can be operated both as a diffusion burner and as a premixing burner. The burner is preferably configured for operation in a gas turbine, in particular, in a stationary gas turbine. Such a burner can, for example, be operated with both mineral oil and natural gas. Preferably, the burner has a central pilot burner that operates as a diffusion burner, i.e., there is no premixing of combustion air and fuel. The central pilot burner is surrounded by a main burner that operates as a premixing burner, i.e., combustion air and fuel are first mixed and subsequently supplied to the combustion process. The diffusion burner preferably has a supply/return nozzle, i.e., the fuel, in particular, mineral oil, enters the nozzle through a supply duct and part of it emerges from the nozzle opening. The remaining part of the fuel is returned through a return line back into a fuel collecting container. In the configuration, the fuel quantity supplied and the fuel quantity returned can each be set by its own control element. The control of the fuel quantity supplied is very complex for such a system. A flexible setting of the degree of opening, as a function of the respective operating conditions, is of particular advantage in this case.
With the objects of the invention in view, there is also provided a burner configuration, including a fuel supply line, an adjustable burner supplied with a quantity of a fuel through the fuel supply line, a control element in the fuel supply line, the control element having a selectable opening for setting the fuel quantity as a function of a selected output of the burner, and a controller connected to the control element. In the controller, the degree of opening can be determined as a function of the output, the type of the fuel, and a pressure loss in the fuel supply line, and a corresponding signal can be transmitted to the control element such that the degree of opening is set.
The advantages of such a burner configuration follow correspondingly from the above statements on the advantages of the method of operating a burner.
Other features that are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method of operating a burner and burner configuration, it is, nevertheless, not intended to be limited to the details shown because various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.